Abstract:

A method and an apparatus enabling use of a light source emitting a
spectrum of light not following characteristics of a blackbody source of
light with a camera module programmed for use with light sources
following characteristics of blackbody sources of light, wherein a
white-balance patch is transmitted to the camera module to cause the
camera module to accept color coordinates representing a point on a
chromaticity chart that partly defines a region of color coordinates on
the chromaticity chart into which color coordinates of the light source
fall and to which color coordinates of a reference white color derived by
a white-balance routine of the camera module are constrained.

Claims:

1. An electronic device comprising:a flash source;a camera module with an
image scanning element and a pre-determined white-balance routine that
includes an initial limit region of a chromaticity chart, the initial
limit region of the chromaticity chart overlying a portion of a blackbody
radiation curve, the flash source having an optical spectrum lying
outside the initial limit region of the chromaticity chart;a storage
containing a white-balance patch and color coordinates of points on the
chromaticity chart; anda processor operable to retrieve the white-balance
patch from the storage and to provide the white-balance patch to the
camera module,the camera module being operable to modify the initial
limit region of the white-balance routine in accordance with the
white-balance patch to obtain a modified limit region, the modified limit
region including at least a portion of the flash source optical
spectrum,the processor also being operable to retrieve the color
coordinates of a first point of the chromaticity chart and to provide the
color coordinates of the first point to the camera module, the first
point being outside the initial limit region and inside the modified
limit region, the first point to be used by the white-balance routine to
define a reference white region, the reference white region excluding any
portion of the black body radiation curve,the processor being further
operable to energize the flash source and to signal the camera module to
activate the image scanning element.

2. The electronic device of claim 1 wherein the flash source is a light
emitting diode and the image scanning element is one of a charge coupled
device and a CMOS imaging device.

5. A method of taking a picture with an electronic device, the electronic
device having a storage containing a white balance patch, a flash source,
and a camera module, the camera module having an image scanning element
and a pre-determined white-balance routine that includes an initial limit
region of a chromaticity chart, the initial limit region of the
chromaticity chart overlying a portion of a blackbody radiation curve,
the flash source having an optical spectrum lying outside the initial
limit region of the chromaticity chart, the method comprising:providing
the white-balance patch to the camera module;modifying the initial limit
region of the white-balance routine in accordance with the white-balance
patch to obtain a modified limit region, the modified limit region
including at least a portion of the flash source optical
spectrum;receiving at the camera module, color coordinates of a first
point of the chromaticity chart, the first point being outside the
initial limit region and inside the modified limit region, the first
point being used by the white-balance routine to define a reference white
region, the reference white region excluding any portion of the black
body radiation curve;energizing the flash source; andsignaling the image
scanning element to scan at least one image.

6. The method of claim 5 further comprising white-balancing the at least
one image in accordance with the reference white region.

7. The method of claim 5 wherein providing the white-balance patch to the
camera module is preceded by retrieving the white-balance patch from the
storage.

8. The method of claim 7 wherein retrieving the white-balance patch from
the storage is preceded by receiving an indication to take the picture.

9. The method of claim 5 wherein energizing the flash source is preceded
by receiving color coordinates of a second point of the chromaticity
chart, the second point being outside the initial limit region and inside
the modified limit region, the second point being used by the
white-balance routine to further define the reference white region.

10. The method of claim 9 wherein the first and second points are
endpoints of a segment of the reference white region.

11. The method of claim 10 further comprising receiving a locus, the locus
being used by the white-balance routine to further define the reference
white region.

12. The method of claim 11 wherein the locus specifies a perpendicular
distance away from the segment.

14. A method of making a camera module compatible with a flash source, the
camera module having a pre-determined white-balance routine that includes
an initial limit region of a chromaticity chart, the initial limit region
of the chromaticity chart overlying a portion of a blackbody radiation
curve, the flash source having an optical spectrum lying outside the
initial limit region of the chromaticity chart, the method comprising, at
the camera module:modifying the initial limit region of the white-balance
routine in accordance with at least one input value to obtain a modified
limit region, the modified limit region including at least a portion of
the flash source optical spectrum; andreceiving color coordinates of a
first point of the chromaticity chart, the first point being outside the
initial limit region and inside the modified limit region, the first
point being used by the white-balance routine to define a reference white
region, the reference white region excluding any portion of the black
body radiation curve.

15. The method of claim 14 wherein the step of modifying the initial limit
region is preceded by receiving the at least one input value.

16. The method of claim 14 further comprising receiving color coordinates
of a second point of the chromaticity chart, the second point being
outside the initial limit region and inside the modified limit region,
the second point being used by the white-balance routine to further
define the reference white region.

17. The method of claim 16 wherein the first and second points are
endpoints of a segment of the reference white region.

18. The method of claim 17 further comprising receiving a locus, the locus
being used by the white-balance routine to further define the reference
white region.

19. The method of claim 18 wherein the locus specifies a perpendicular
distance away from the segment.

Description:

[0001]This application is a continuation of U.S. application Ser. No.
11/626,886 filed Jan. 25, 2007 the contents of which are incorporated by
reference in their entirety.

BACKGROUND

[0002]1. Field

[0003]The disclosed and claimed concept relates generally to electronic
devices and, more particularly, to a method for controlling a camera
module incorporated into a portable electronic device to compensate for
the characteristics of a white LED used as a flash for taking pictures.

[0004]2. Description of the Related Art

[0005]It is widely known to use a variety of different sources of light
for taking a picture with a digital camera module, including natural
sunlight, a xenon strobe, an incandescent bulb or a fluorescent bulb.
Despite being very different light sources using very different processes
to emit light, a common characteristic of all of these light sources is
that the spectrums of light emitted by each of them, despite being
different, provide a range of light frequencies that resemble the
expected behavior of radiant emissions of a blackbody at given
temperatures.

[0006]In 1931, an international committee called the Commission
Internationale de L'Eclairage (CIE) met in Cambridge, England, and
attempted to put forward a graphical depiction of the full range of
colors of light that the human eye can actually perceive. This graphical
depiction, namely a chromaticity chart, and the resulting standard
incorporating this chromaticity chart has come to be known as "CIE 1931"
and is widely used by scientists and photographers, among many others, in
working with light in the visible light spectrum. FIG. 1 depicts a
simplified representation of a chromaticity chart 100 based on the CIE
1931 standard, with all visible colors of light specifiable with two
dimensional color coordinates. As can be seen, towards the center of what
is frequently called the "horseshoe-shaped" visible region 110 of all
that the human eye can perceive is a white region 120 of colors of light
generally categorized as "white light" and surrounded by other regions
generally described as non-white light, including a red region 121, a
pink region 122 and a purple region 123. It should be noted that the
exact boundaries of these regions 120-123 should be taken as
approximations and not precise designations of color, since the
classification of colors is necessarily subjective.

[0007]The human brain has evolved its own form of white-balancing
capability by which human beings have little trouble discerning what
color an object should be, even though it may be illuminated with light
that is only marginally white, such as the reddish hue of the sun at
sunset, the orange glow of campfire, or the bluish tint of a mercury
vapor streetlight. It is due to this flexibility of the human brain that
a number of light sources emitting a variety of different spectra of
light, and thereby having a variety of differing color coordinates that
occupy different points on a chromaticity chart, can be classified as
"white" light sources with the result that the white region 120 in FIG. 1
occupies a considerable proportion of the visible region 110.

[0008]Passing through the white region 120 is a portion of a blackbody
curve 130 depicting the set of color coordinates of white light sources
that emit a spectrum of light frequencies that substantially follow the
spectrum of light frequencies that would be expected to be emitted from
theoretically ideal blackbody light sources heated to different
temperatures. Most commonly used sources of white light have color
coordinates specifying a point that falls along or substantially close to
this blackbody curve 130, including sunlight and xenon flash strobes, as
well as incandescent, fluorescent, high-pressure sodium and mercury vapor
lamps. As a result of so many of the commonly used sources of light used
in taking pictures having color coordinates representing points that fall
on or relatively close to the blackbody curve 130, algorithms, constants
and limit values employed in digital cameras to perform automatic
exposure control and automatic white-balancing are commonly chosen and
designed with a presumption that all light sources that will be
encountered will be ones with such color coordinates. Indeed, this
presumption has become so ingrained that it has become commonplace for
manufacturers of camera modules incorporated into other electronic
devices to have such choices of algorithms, constants and limit values
built into or preprogrammed directly into the camera modules, themselves.

[0009]As those skilled in the art of white-balancing algorithms will
recognize, a step taken by many known white-balancing algorithms is
attempting to derive a reference white color in a given image as an input
parameter for determining the degree to which the colors in that image
are to be adjusted to compensate for the lighting in the original scene
so that the objects in the resulting picture are presented with their
correct colors. To do this, white-balancing algorithms typically require
either that there be an object in the image that actually is white (known
as the "white world" algorithm) or that the average of all the colors of
all the pixels in the image be a gray (known as the "gray world"
algorithm), and either of these approaches can provide a basis from which
a reference white color for that image may be derived. However, it is
possible to have images that do not provide a white object or that are
filled with objects of colors that provide a very skewed result when
averaging to derive a gray. An example of such an image is one filled
with the tree leaves of a forest of trees such that the image is filled
with different shades of green and little else, thereby providing no
white objects and providing an average that will necessarily be a green
color and not a gray. If white-balancing algorithms are allowed to
process such an image without constraints, the result can be whited-out
or blackened-out objects in the resulting picture, and so it is deemed
desirable to specify boundaries for what a reference white color may be
so as to constrain the degree to which a white-balancing algorithm is
permitted to adjust colors.

[0010]Given the aforementioned presumption that the light sources to be
encountered by a digital camera are likely to have color coordinates
specifying points falling along or quite close to the blackbody curve
130, the format in which the boundaries for what a reference white color
may be are communicated to typical camera modules in a manner that
comports with this assumption. In this commonly used format, a pair of
color coordinates that define the endpoints of a straight segment in a
chromaticity chart, such as a segment 140 depicted in FIG. 1, are
communicated to a camera module along with an error term (or "locus")
specified in terms of a maximum perpendicular distance away from the
segment 140. These two endpoints and the error term, together, specify a
rectangular-shaped reference white region 141 within the white region 110
that defines these boundaries, thereby defining a set of acceptable color
coordinates within which the white-balancing algorithm is permitted to
choose a color to be a reference white for a given image. This is to
allow a short segment that should resemble a small portion of the
blackbody curve 130 to be specified, such as segment 140, and this short
segment should be positioned to either largely overlie a portion of the
blackbody curve 130 or to be relatively close to and relatively parallel
with a portion of the blackbody curve 130. No allowance is made in this
format for specifying the boundaries of a possible reference white with a
reference white region having any other shape than a rectangular region,
such as the reference white region 141 shown.

[0011]Also, given the same aforementioned presumption that the light
sources to be encountered by a digital camera are likely to have color
coordinates specifying points falling along or quite close to the
blackbody curve 130, it is commonplace to in some way build minimum
and/or maximum limits on values used to define the reference white region
141 such that values defining a reference white region 141 that does not
substantially overlie the blackbody curve 130, or that is not at least
substantially close to the blackbody curve 130 are rejected. The
effective result is to create a limit region, such as limit region 145
depicted in FIG. 1, into which at least a portion of the white region 141
must fall.

[0012]Of those light sources having color coordinates representing points
falling along or close to the blackbody curve 130, xenon strobes have
become commonplace for use as flashes in portable electronic devices used
in photography. A xenon strobe is very small in size while producing an
extremely bright light that very quickly illuminates a setting of which a
picture is to be taken. The amount of illumination needed from a flash to
sufficiently light a scene for scanning its image is a measurable
quantity and can be roughly calculated as the brightness of the flash
multiplied by the amount of time it must be turned on. The brighter the
light source used as a flash, the less time it needs to be turned on to
sufficiently light a scene. Furthermore, the amount of time that a given
flash needs to be turned is not necessarily related to the amount of time
needed for an image scanning element (such as a CCD semiconductor device
or a CMOS imaging device) to actually scan an image as part of the
process of capturing that image. In other words, where a bright flash is
used, it is not unheard of to actually turn off the flash before the
image scanning element has completed scanning the image, because a
sufficient amount of illumination has been supplied and leaving the flash
on any longer would result in too high an amount of illumination and
portions of the image being whited out. However, where a dimmer light
source is used as a flash, the flash must be turned on for a longer
period of time to achieve the same amount of illumination as a brighter
light source, and it is often necessary to delay the start of scanning an
image until a high enough amount of illumination has been achieved.

[0013]Recently, a new artificial source of white light, the so-called
white LED, has been introduced, providing the opportunity to create a
flash for use in digital photography that requires less power than other
light sources. Unfortunately, the white LEDs have a range of color
coordinates specifying a range of points that fall substantially distant
from the blackbody curve 130, and furthermore, at least partly fall
outside the white region 120 and into the pink region 122. This deviation
of white LEDs from the blackbody curve 130 is largely due to the manner
in which white LEDs produce light. White LEDs are in truth, blue LEDs
that are partially covered with a yellowish phosphor that converts part
of the blue light into yellow light. The result is a blending of blue and
yellow light frequencies that approximates white light well enough for
the human eye and the human brain to accept it as a source of white
light. In essence, two different non-white light emissions, each having
its own spectrum of light frequencies, are being blended to approximate
white light and such a mixing of two non-white spectra is not
characteristic of blackbody sources of radiant energy.

[0014]Also, white LEDs, though brighter than incandescent lamps of
comparable size, are far dimmer than xenon strobes of comparable size. As
a result, to achieve a desirable amount of illumination of a scene when
used as a flash, a white LED must be kept on far longer than a xenon
strobe used as a flash, and a white LED must also be supplied with a very
high amount of electric power that would actually damage internal
components of the white LED if that amount of power were maintained for
more than a very brief period of time. In using a white LED as a flash,
the amount of time during which the white LED is actually turned on can
be kept short enough to prevent this damage. Unfortunately, even during
the brief period in which the white LED is turned on, the light emitting
semiconductor components of the white LED respond to the very high amount
of power by converting an ever increasing proportion of that power into
heat as time passes from the moment at which that power is first supplied
to the moment when that power is removed. Correspondingly, as time passes
the proportion of that power converted to visible light decreases such
that the white LED is initially very bright when that power is first
applied, but that brightness level almost immediately begins fading more
and more as time passes. With this quickly fading of brightness, the
color spectrum output by a white LED also changes quickly as time passes
from the moment that it is turned on. This changing light level and this
changing color spectrum must be taken into account in both calculating
the amount of time a white LED is to be turned on to provide a sufficient
total amount of illumination to serve as an effective flash and in
compensating for its changing spectrum of light output in performing
white-balancing.

[0015]Another feature of white LEDs not exhibited by artificial light
sources long used in photography, including xenon strobes and
incandescent bulbs, is the high variability in the color spectra of each
of the blue and yellow elements of the light emitted by white LEDs. White
LEDs and the technology to manufacture them are still sufficiently new
that only slow progress has been made in exerting tighter control over
the manufacture of white LEDs to achieve sufficient consistency to avoid
having two white LEDs from the very same production run emit light that
is of perceptibly different hues. For this reason, unlike other
artificial light sources that have far higher consistency in the spectra
of their emitted light, the size of the region of that the "white" light
emitted by LEDs may fall within is considerably larger than for other
light sources. As a result of these various issues, current practices in
controlling a camera module's built-in white-balancing algorithm are
insufficient to accommodate the very unique characteristics of white
LEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]A full understanding of the disclosed and claimed concept can be
gained from the following Description when read in conjunction with the
accompanying drawings in which:

[0017]FIG. 1 is a simplified depiction of a CIE 1931 chromaticity chart
depicting the black body curve and a PRIOR ART approach to specifying a
reference white region within which a reference white color is
constrained;

[0018]FIG. 2 is a depiction of an improved handheld electronic device in
accordance with the disclosed and claimed concept;

[0019]FIG. 3 is a schematic depiction of the improved handheld electronic
device of FIG. 2;

[0020]FIG. 4 is another simplified depiction of a CIE 1931 chromaticity
chart depicting the black body curve and an approach to specifying a
reference white region within which a reference white color is
constrained in accordance with the disclosed and claimed concept; and

[0021]FIG. 5 is a flowchart depicting an embodiment of an improved method
in accordance with the disclosed and claimed concept.

DESCRIPTION

[0022]The accompanying figures and the description that follows set forth
the disclosed and claimed concept in its preferred embodiments. It is,
however, contemplated that persons generally familiar with handheld
electronic devices will be able to apply the novel characteristics of the
structures and methods illustrated and described herein in other contexts
by modification of certain details. Accordingly, the figures and
description are not to be taken as restrictive on the scope of the
disclosed and claimed concept, but are to be understood as broad and
general teachings.

[0023]For purposes of the description hereinafter, the terms "upper",
"lower", "right", "left", "vertical", "horizontal", "top", "bottom", and
derivatives thereof shall relate to the disclosed and claimed concept as
it is oriented in the figures.

[0024]An improved electronic device 200 is depicted generally in FIG. 2
and is depicted schematically in FIG. 3. The electronic device 200 may be
a handheld or other portable electronic device (e.g. and without
limitation, a digital camera, a PDA, a cell phone, a digital watch, or a
laptop computer). The electronic device 200 incorporates a housing 202 on
which are disposed a white LED 207 serving as a flash for taking pictures
and a camera module 250. The housing 202 may additionally have disposed
thereon an input device 204 and/or an output device 205. The electronic
device 200 also incorporates a processor 210 connected to a storage 220,
and a LED interface 237 controlling the LED 207. The processor 210 may
additionally be connected to one or more of an input interface 234
receiving input from the input device 204, an output interface providing
output to the output device 205, and a media storage device 240 capable
of interacting with a storage medium 241 (which may or may not be of
removable form). The camera module 250 incorporates a processor 260
connected to a storage 270, an exposure control element 282 and an image
scanning element 283. Although described and depicted as being disposed
on the housing 202 of the electronic device 200, the white LED 207 and/or
the camera module 250 may alternatively be physically separate from the
housing 202, but linked to other components of the electronic device 200
through a suitable electrical, optical, radio frequency or other linkage.

[0025]The processors 210 and 260 may be of any of a wide variety of
processing devices, including and without limitation, microcontrollers,
microprocessors, sequencers, digital signal processors or state machines
implemented in hardware logic. In some embodiments, one or both of the
processors 210 and 260 may be one of a number of commercially available
processors executing at least a portion of the widely known and used
"X86" instruction set and/or another instruction set.

[0026]The media device 240 and the storages 220 and 270 may be of any of a
wide variety of types of storage devices, including and without
limitation, disk drives (e.g. and without limitation, hard drives, floppy
drives, magneto-optical drives, magnetic tape drives or CD-ROM drives),
solid state memory (e.g. and without limitation, static RAM, dynamic RAM,
ROM, EEPROM or FLASH) and memory card readers. However, in preferred
practice, the storages 220 and 270 are generally more capable of
supporting speedy random accesses than the media device 240, and the
media device 240 is capable of supporting removable media while the
storages 220 and 270 are not meant to be removable. In preferred
practice, it is generally intended that the removable media device 240
support the exchange of data and/or software between the electronic
device 200 and another electronic device (not shown) through the storage
medium 241.

[0027]The white LED 207 may be any of a variety of semiconductor-based
light emitting diodes capable of emitting light that substantially
approximates white light. The white LED 207 may be fabricated by applying
a coating to a blue LED that converts at least some of the emitted blue
light into a yellow light such that a combination of blue and yellow
light is produced that approximates white light to the perception of the
human eye. Alternatively, the white LED 207 may be fabricated in other
ways as those skilled in the art will readily recognize, including, but
not limited to, adding or applying red and green phosphors to a blue LED.
The LED interface 237 allows the processor 210 to control when the white
LED 207 is turned on and may allow the processor 210 to control the
intensity of the light emitted by the white LED 207.

[0028]The camera module 250 may be any of a variety of commercially
available camera modules fabricated by a variety of manufacturers for the
purpose of being incorporated into other devices, such as the electronic
device 200. The image scanning element 283 may be one of a variety of
available charge-coupled devices (CCD) or CMOS imaging devices, or may be
another suitable form of device capable of scanning an image of objects
in its view. The exposure control element 282 provides an aperture of
controllable dimensions through which the light from the objects in the
view of the image scanning element 283 passes to reach the image scanning
element 283. Alternatively, the exposure control element 282 may control
the amount of light reaching the image scanning element 283 in other ways
known to those skilled in the art.

[0029]The input device 204 may be of any of a variety of input devices
capable of accepting input from a user of the electronic device 200,
including without limitation switches, a keypad, a joystick, a
rollerball, or a touchpad. In embodiments that incorporate the input
device 204, the input interface 234 couples the processor 210 to the
input device 204 to receive input therefrom. The output device 205 may be
of any of a variety of output devices capable of providing information to
a user of the electronic device 200, including without limitation lights,
a display device, an audible indicator, or a tactile device such as a
vibrator mechanism causing the electronic device 200 to vibrate such that
a user of the electronic device 200 is able to feel the vibration. In
embodiments that incorporate the output device 205, the output interface
235 couples the processor 210 to the input device 205 to provide output
thereto.

[0030]When the electronic device 200 is used to take a picture, the
processor 210 accesses the storage 220 to retrieve and execute a sequence
of instructions of a control program 222, thereby causing the processor
210 to transmit sequences of instructions and/or data to the camera
module 250 and to operate the camera module to scan one or more images as
will shortly be explained. In turn, the processor 260 accesses the
storage 270 to retrieve and execute sequences of instructions from a
white-balance routine 272, an exposure routine 274 and/or another
sequence of instructions provided by the processor 210, thereby causing
the processor 260 to operate the exposure control element 282 and the
image scanning element 283 to carry out the scanning of one or more
images. The processors 210 and 260 are caused to interact to transfer the
data representing the resulting picture from the camera module 250 to be
stored in the storage 220, or perhaps the media storage device 240 if
present. Where the taking of a picture entails the use of the white LED
207 as a flash, the processors 210 and 260 may be caused to further
interact in controlling the timing and intensity of the lighting supplied
by the white LED 207 through the LED interface 237.

[0031]In embodiments of the electronic device 200 having the input device
204 and/or the output device 205, the processor 210 is further caused by
the control program 222 to operate the input interface 234 and/or the
output interface 235 to interact with the user of the electronic device
200 through one or both of the input device 204 and the output device
205. Where the input device 204 includes a relatively small number of
switches providing the user with the ability to control various aspects
of the process of taking a picture (e.g. without limitation, the focus,
the landscape or portrait mode, and whether or not to use a flash), the
processor 210 receives such input from the user and carries out the
taking of a picture, accordingly. Where the input device 204 includes a
keypad or other device providing greater flexibility of input, the user
may be provided with the ability to enter data concerning the picture to
be taken, such as a time, place or name of the subject of the picture.
Where the output device 205 includes a graphical display, the processor
210 may be caused by the control program 222 to present the user with a
view of what the image scanning element 283 sees before the picture is
taken and/or a view of the resulting picture on the output device 205.

[0032]In embodiments of the electronic device 200 having the media storage
device 240, the processor 210 may be further caused to store pictures
taken by the user on the storage medium 241 for the user to transfer to
another electronic device (not shown) for display, archiving and/or
printing. Where such embodiments also incorporate a form of both the
input device 204 and the output device 205 of sufficient ability, the
processor 210 may be further caused to provide the user of the electronic
device 200 with the ability to use the input device 204 and the output
device 205 to view and select pictures to be stored on the storage medium
241, as well as to select pictures to be deleted. Alternatively, or in
addition to the media storage device 240, the electronic device 200 may
further incorporate a communications interface (not shown) allowing the
electronic device 200 to be directly connected to another electronic
device for the transferring of pictures, other data and/or software (e.g.
without limitation, a digital serial interface such as IEEE 1394).

[0033]As previously described, the camera module 250 may be any one of a
variety of commercially available camera modules from a variety of
manufacturers for incorporation into various electronic devices,
including the electronic device 200. The white-balance routine 272 may be
based on any of a variety of widely known white-balancing algorithms
(including the earlier-described gray world and white world algorithms)
to derive a reference white color for a given image that is used to
determine the degree to which the white-balance routine 272 is to be used
to modify that image to compensate for the lighting used. However, as was
also previously described, it is common practice to impose constraints on
white-balancing algorithms to prevent overcompensation for lighting that
can result where the colors in an image do not provide white-balancing
algorithms with the reference colors needed to function, correctly.

[0034]Unfortunately, the commonplace manner of describing the reference
white region of color coordinates to which the point representing a
reference white color is to be constrained as a rectangular region that
is substantially adjacent to or that substantially overlies a portion of
a blackbody curve on a chromaticity chart is based on the assumption that
whatever source of light is used to illuminate an image will exhibit
characteristics largely conforming to what would be expected of a
corresponding blackbody source of radiation. This same assumption has
also resulted in the commonplace practice of incorporating into a
parameter data 273 within the storage 270 a set of minimum and maximum
value limits that will be accepted for specifying the color coordinates
defining the segment that partly defines that rectangular region. In
effect, these minimum and maximum value limits describe a limit region
into which at least a portion of the white reference region must fall.
Unfortunately, to describe a rectangular region within which the color
coordinates of the white LED 207 are likely to fall requires specifying
color coordinates that are outside such minimum and maximum value limits.

[0035]As part of the earlier-described process of taking a picture where
the white LED 207 is employed as a flash, the processor 210 is caused by
the control program 222 to provide the camera module 250 with a pair of
color coordinates (i.e., the pair of points defining a segment) and an
error term (or "locus") that define a rectangularly-shaped reference
white region to which the point defined by the color coordinates of the
reference white color derived by the white-balance routine 272 are to be
constrained. However, to overcome the commonplace limitations imposed by
the minimum and maximum value limits stored within the parameter data
273, the processor 210 is first caused by the control program 222 to
transmit to the camera module 250 a white-balance patch 225 retrieved by
the processor 210 from the storage 220. In some embodiments, the
white-balance patch 225 provides at least one alternate minimum and/or
maximum value that the processor 260 uses in place of at least one
minimum and/or maximum value of the parameter data 273 when executing a
sequence of instructions of the white-balance routine 272. In other
embodiments, the white-balance patch 225 provides an alternate sequence
of instructions to be executed by the processor 260 in place of at least
a portion of a sequence of instructions of the white-balance routine 272.
In still other embodiments, both alternate value(s) and alternate
instructions are provided. In effect, these alternate value(s) and/or
instructions redefine the boundaries of the limit region into which at
least a portion of a reference white region must fall. This redefining
may entail resizing the limit region, may entail shifting the position of
the limit region on a chromaticity chart, or may entail both.

[0036]FIG. 4 depicts a chromaticity chart 150, that when compared to the
chromaticity chart 100 of FIG. 1, illustrates the change enabled with
transmission of the white-balance patch 225 to the camera module 250.
Upon receiving the white-balance patch 225, the limit region 145 of
chromaticity chart 100 is redefined to create an alternate limit region
195 such that the camera module 250 is able to accept a pair of color
coordinates defining a pair of points that define an alternate segment
190, that along with an appropriate error term, define a
rectangularly-shaped alternate reference white region 191. The alternate
reference white region 191 defines the constraints to which color
coordinates specifying a point for a reference white color that better
corresponds with the use of the white LED 207 will be held. As can be
seen, unlike the reference white region 141, at least a portion of the
alternate reference white region 191 lies outside the limit region 145
and the alternate reference white region 191 neither overlies nor is
substantially adjacent to the blackbody curve 130.

[0037]It should be noted that although the alternate limit region 195 is
depicted as a tilted rectangular region not unlike the reference white
region 191, other configurations of the limit region 195 are possible as
those skilled in the art will readily recognize. Furthermore, in various
embodiments, the alternate limit region 195 may represent an expansion of
the limit region 145, a shifting of the limit region 145, a replacement
of the limit region 145, a provision of an alternate limit region in
addition to the limit region 145, or other form of redefinition of the
limit region 145 as those skilled in the art will readily recognize.

[0038]As also previously discussed, the white LED 207 is a dimmer source
of visible light than a xenon strobe, requiring that the white LED 207
remain turned on longer than a xenon strobe to achieve a comparable
amount of illumination in illuminating a scene. However, even though this
longer period is still short enough to be perceived by the human eye as a
mere flash, it is long enough for the level of visible light output by
the white LED 207 to fade significantly from the time the white LED 207
is first turned to the time the white LED 207 is turned off. This
changing light level adds complexity to the operation of the exposure
routine 274 that causes the processor 260 to control the exposure control
element 282 to adjust the amount of light received by the image scanning
element 283 in taking a picture. Also, as those skilled in the art will
readily recognize, a changing light level from a light source also
results in a changing color spectrum for the light output by that light
source, and this adds complexity to the operation of the white-balance
routine 272. To address the changing light level and the changing color
spectrum occurring during use of the white LED 207 as a flash, the
processor 210 is caused by the control program 222 to operate the camera
module 250 in a mode that is normally reserved for use in lighting
conditions in which no flash is used.

[0039]In the prior art digital cameras, it is commonplace to operate a
camera module to scan a single image when a flash is used, and to operate
a camera module to scan a succession of images when a flash is not used.
With light sources that might be used as a flash, other than a white LED,
the characteristics of the spectrum of light emitted are more tightly
controllable, are more consistent and are far better known given the many
years that other light sources have been used in photography. Therefore,
a camera module may be given a set of highly reliable initial values as
inputs to white-balancing and/or exposure algorithms with considerable
confidence that those values are likely to be correct enough for most
forms of scenery such that an image of that scenery need be scanned only
once. However, where a flash is not used, the lighting within the scene,
itself, is being relied upon to provide the necessary illumination, and
unlike a flash incorporated into a digital camera, the characteristics of
that lighting cannot be described to the camera module with such
precision. Therefore, it is commonplace to supply the camera module with
a highly general set of initial values that are deemed most likely to be
applicable to most situations, and to then scan a rapid succession of
images when the user of the digital camera presses a button to take a
picture. With each successive image, the initial values are adjusted
based on an analysis of the results of applying the initial values to the
preceding image.

[0040]It should be noted that part of the reason that the scanning of
multiple images is necessary to support the successive use of
white-balancing and/or exposure algorithms is that it is commonplace
practice to keep the costs of camera modules low by not incorporating a
frame buffer into camera modules. In other words, white-balancing and
exposure algorithms must be applied to the pixels of an image as the
image seen by a camera module's image scanning element is scanned by the
image scanning element. If a frame buffer capable of holding an entire
scanned image were incorporated into a camera module, it would be
possible to actually capture an image (wherein capturing an image entails
both scanning and storing the image, and not merely scanning it) and
repeatedly apply white-balancing and/or exposure algorithms to the single
captured image while refining the initial values with each application of
those algorithms. The scanning of the 3, 4, 5 or possibly more images
occurs quickly enough that the user of the digital camera does not
realize that multiple images are being scanned in taking a single
picture, but with the scanning of a succession of images, the
white-balancing and/or exposure algorithms are provided with multiple
opportunities to more precisely compensate for unknown lighting
conditions.

[0041]As part of the earlier-described process of taking a picture where
the white LED 207 is employed as a flash, the processor 210 is caused by
the control program 222 to operate the camera module 250 as if a picture
without a flash were being taken such that the camera module 250 is
caused to scan a succession of images. The processor 210 is caused to
supply the camera module 250 with initial values to be employed by the
processor 260 in executing sequences of instructions from the
white-balance routine 272 and/or the exposure routine 274. Unlike a
situation in which lighting with unknown characteristics at a scene is
employed, the characteristics of the white LED 207 are known, although
some of those characteristics are expected to vary. Also, the processor
210 may be caused to perform one or more calculations to derive one or
more of the initial values based on one or more inputs, such as a manual
setting regarding light levels or exposure time provided by a user of the
electronic device 200, or an input from a light level sensor (not shown).

[0042]The processor 210 then directs the camera module 250 to begin
scanning a succession of images of a scene and the processor 210 operates
the LED interface 237 to turn on the white LED 207. Use is made of the
fact that the white LED 207 is sufficiently dim that the white LED 207
will have to be turned on for a period of time long enough that a number
of images can easily be scanned by the camera module 250 while the LED
207 is still turned on. The scanning of images is directed by the
processor 210 to begin within a very short period of time after the white
LED 207 is turned on. Although this results in a relatively small amount
of illumination having been applied to a scene at the time the first
image is scanned, such an initial amount of lighting is sufficient for
the processor 260 to execute sequences of instructions of the
white-balance routine 272 and/or the exposure routine 274 to begin the
process of refining the initial values to compensate for the light
provided by the white LED 207. As each successive image is scanned, more
time passes during which the white LED 207 is turned on and more of the
total illumination required to fully illuminate a given scene is supplied
by the white LED 207.

[0043]During the scanning of these successive images, the spectrum of
light provided by the white LED 207 changes as an increasing proportion
of the electrical energy supplied to the white LED 207 is converted to
heat (instead of visible light) over time. However, the degree of change
in the spectrum between the scans of successive images is small enough
that the process of successive refinement of the initial values is able
to compensate for it. In some embodiments, the quantity of successive
images to be scanned is a set value preprogrammed into the camera module
250. In other embodiments, the degree to which the initial values are
changed with each refinement accompanying the scanning of each successive
image is analyzed to determine if the degree of change has reached a low
enough threshold level between the two most recently scanned images that
there is unlikely to be further significant refinement with the scanning
of any more images.

[0044]FIG. 5 is a flow chart of an embodiment of an electronic device with
a white LED and a camera module being used to take a picture. Starting at
510, the electronic device awaits an indication from a user of the
electronic device to take a picture. Such an indication may be supplied
by the user pressing a button disposed on the housing of the electronic
device, a timer set by the user, or another mechanism under the user's
control. At 520, the next step is determined by whether or not the white
LED of the electronic device is used as a flash in taking the picture.
Whether or not the white LED is used may be determined by an input
provided by the user (e.g., without limitation, a switch operated by the
user to control use of the white LED) or by an automated function of the
electronic device in which the white LED is employed as a flash if a
sensor of the electronic device detects insufficient light to take the
picture without using the white LED.

[0045]If at 520, the white LED is not used as a flash, then a set of
general initial values applicable to a wide variety of possible light
sources that may be present in a given scene are transmitted to the
camera module at 530. Given that natural sunlight is highly likely to be
the source of light relied upon in such circumstances, the initial values
are likely to be chosen to prepare the light-balancing and/or exposure
routines of the camera module for a light source having characteristics
consistent with a blackbody source of light. One or more of the initial
values may be derived and/or modified by a processor of the electronic
device into which the camera module is incorporated to take into account
input from a light level sensor providing an indication of the amount of
light available in the given scene.

[0046]At 532, the electronic device signals the camera module to scan a
succession of images. As discussed earlier, repetitive application of
white-balancing and/or exposure routines allows greater refinement of the
initial values, and the scanning of a succession of images of a given
scene is necessary for a camera module having no frame buffer in which a
single complete scanned image could be stored (such that the image could
be said to have been "captured" rather than simply scanned) to allow the
white-balancing and/or exposure routines to be repeatedly applied to a
single captured image.

[0047]However, if at 520, the white LED is used as a flash, then a
white-balance patch is transmitted to the camera module at 540. As
previously discussed, it is common practice for camera modules to be
programmed with minimum and maximum limits for initial values transmitted
to the camera module by the electronic device that are based on the
assumption that all light sources will exhibit characteristics consistent
with a blackbody source of light. These initial values include values
defining a reference white region on a chromaticity chart into which the
point specified by the color coordinates of a reference white color
derived by the camera module's white-balancing routine must fall.
However, as previously discussed, the typical minimum and maximum limits
for these initial values define a limit region that does not permit color
coordinates defining a reference white region at a location more
appropriate for a white LED to be specified. The white-balance patch
transmitted at 540 provides the camera module with at least one alternate
minimum/maximum value more appropriate for those color coordinates and/or
provides a substitute sequence of instructions to be executed by a
processor within the camera module in place of at least a portion of the
camera module's white-balancing routine.

[0048]At 542, initial values corresponding to the use of the white LED are
transmitted to the camera module, including a pair of segments and an
error term defining a reference white region into which the point denoted
by the color coordinates of a derived reference white color will be
constrained. At 544, the electronic device signals the camera module to
scan a succession of images. During the scanning of those images, the
initial values corresponding to the use of the white LED are further
refined to allow more precise compensation for the changing light
provided by the white LED. At 546, with the picture having been taken,
the electronic device may transmit a signal to the camera module causing
the erasure of the white-balance patch from a storage within the camera
module, or causing some other action to occur that counteracts the
white-balance patch.

[0049]While specific embodiments of the disclosed and claimed concept have
been described in detail, it will be appreciated by those skilled in the
art that various modifications and alternatives to those details could be
developed in light of the overall teachings of the disclosure.
Accordingly, the particular arrangements disclosed are meant to be
illustrative only and not limiting as to the scope of the disclosed and
claimed concept which is to be given the full breadth of the claims
appended and any and all equivalents thereof.